This invention relates to cutting inserts and more particularly to cutting inserts for presenting positive back and side rake angles to a workpiece. Even more particularly, the invention relates to inserts capable of providing the above function while positioned within a negative rake tool holder.
Among the most widely used tool holders in the metal cutting art are those commonly referred to as negative rake tool holders. Such devices present a negative back and side rake angle to the workpiece surface when positioned relative thereto. Accordingly, it has become a common practice to utilize a negative rake angle cutting insert with said negative rake tool holder when performing a desired cutting operation. An example of such a component is fully illustrated in U.S. Pat. No. 3,381,349 wherein an indexable insert is utilized in conjunction with the previously described negative rake tool holder.
With regard to the aforementioned back and side rake angles, is is to be understood that back rake is the angle between the cutting edge of the tool and a perpendicular to the surface of the workpiece being cut. If the back rake angle is on the side of the perpendicular toward which the workpiece surface is moving, the rake angle is defined as being positive. If this angle lies on the opposing side of the perpendicular, the back rake angle is defined as being negative. The aforementioned side rake angle is that angle between the surface of the insert which receives the cut chips from the workpiece and the direction of the insert across the workpiece surface. Similar to the back rake designation, if the angle of the side rake lies on the side of the direction of feed toward which the workpiece surface is moving, the side rake is defined as positive. Accordingly, if it lies on the opposing side of the direction of feed, it is defined as being negative.
It is acknowledged that cutting inserts adaptable for presenting positive back and side rake angles to a workpiece surface when positioned in negative rake holders are known in the art. A typical example of such an insert is illustrated in U.S. Pat. No. 3,399,442. As described therein, it is desirable to form the groove portion of this insert in a concave direction toward one of the insert's faces. As further explained, the described concave formation is achieved by curving the outer region of the insert's recess either spherically or cylindrically to improve chip control. U.S. Pat. No. 3,399,442 further describes a smooth inward extension of the inner recessed portion of the insert to also assist in chip control.
While this and similar cutting devices have improved the metal cutting art, there still exists a need for more positive chip control. It has still been found that chips of relatively extensive helical length are produced when utilizing the devices described above. As can be appreciated, chips of this nature not only impede the cutting process but also present a potential hazard to the tool operator.
It is believed therefore that a cutting insert which provides the operational advantages of being positive in back and side rake angles when positioned within a negative rake tool holder in addition to significantly improving chip control and removal from the surface of a workpiece being cut would constitute an advancement in the art.